1. Field of the Invention
This invention relates to a floating type web guiding device which conveys a long belt-like material (hereinafter referred to as "a web"), while floating it above its guide surface. This device is used in the manufacture of photographic photosensitive materials such as photographic films and print paper, photomechanical process materials, magnetic recording materials such as magnetic recording tapes, or recording materials such as pressure-sensitive copying sheets or heat-sensitive copying sheets.
2. Background of the Invention
A floating type web guiding device is well known in the art in which a web is conveyed along a guide surface having fluid jetting holes or slits. The web is conveyed while being floatd above the guide surface. The guide surface is arcuate in section so that the direction of conveyance of the web is changed while the web is run along the curved guide surface.
In the floating type web guiding device, the web is stably floated above the guide surface in the case where the radius of the guide surface arcuate in section is large and the tension of the web is low. On the other hand, in the case where the radius of the guide surface is small and the tension of the web is high, in order to float the web above the guide surface it is necessary to increase the pressure of the fluid serving as cushion between the web and the guide surface. When the high pressure fluid between the web and the guide surface is discharged from between there at a web lead-in part or a web lead-out part of the guide surface through which the web is led into or out of the space over the guide surface, the web is greatly vibrated or fluttered. As a result, the web may be brought into contact with the guide surface.
In order to prevent the fluttering of the web, a device has been proposed by Japanese Patent Application (OPI) No. 93056/1985. In the conventional device, guide boards are extended in the direction of movement of the web and along the guide surface.
It is true that the device is effective in supressing the fluttering of the web. However, the device is still disadvantageous in that the venturi effect is produced between the web and the guide boards, so that the pressure of fluid between the web and the guide boards is decreased and accordingly the amount of floating of the web is reduced. Therefore, in the case where, for instance, a curled web is conveyed by the device, the web is liable to contact the guide boards, and the manufactured product may not have acceptable quality.